Modern computer drawing and modelling programs (usually known as "computer assisted design" or "CAD" programs) can display complicated three-dimensional objects in great detail, can generate shadows showing the appearance of the object in various types and directions of lighting, and permit the observer to rotate the three-dimensional object about any axis, so that he can see any desired aspect of the object. So realistic are the images produced by sophisticated CAD programs that it is difficult for the user not to believe that he is watching a real object rather than just a computer simulation of a non-existent object. (Hereinafter for convenience, the term "real object" will be used to denote an object which physically exists in space-time, while the term "virtual object" will be used to denote a model which exists only as a mathematical construct in a computer.)
Unfortunately, when the user of a CAD program wishes to produce a hard copy of a three-dimensional virtual object, he finds that most available forms of output are essentially two-dimensional. Typically, the user will generate a hard copy of his results as a series of two-dimensional sections through the object. While such a series of sections may be convenient for preparing working drawings for manufacture of the corresponding real object, such a series does not readily convey an idea of the three-dimensional structure of the virtual object to most observers, particularly those not skilled in interpreting technical drawings.
Alternatively a series of images of the virtual object (showing, for example, rotation of the object about one or more axes) may be recorded on video tape. However, not only is special equipment needed to convert computer data to conventional video standards, but the resultant video images are typically of low resolution, and restrict an observer of the tape to watching a series of two-dimensional views of the virtual object chosen and fixed by the program's user, rather than allowing the observer to choose his own selection and sequence of views of the virtual object.
Holographic techniques can of course record full details of a three-dimensional virtual object and permit an observer to view the hologram as if it were a three-dimensional real object. However, holographic recording requires the use of a laser, and holograms of a type which can be viewed in white light display distracting color changes as the parallax of the hologram is observed.
Various techniques are known for recording three-dimensional images in lenticular media having one or more photosensitive layers. As early as 1908, Gabriel Lippman invented a method for producing a true three-dimensional image of a scene with vertical and horizontal parallax; see, for example, De Montebello, "Processing and Display of Three-Dimensional Data II" in Proceedings of SPIE, San Diego, 1984. In Lippman's method, a photographic plate is exposed through a "fly's eye" lens sheet, so that each lenslet forms a miniature image of the scene being reproduced, as seen from the perspective of the point on the sheet occupied by that lenslet. After the photographic plate has been developed, an observer looking at the composite image on the plate through the lenticular sheet sees a three-dimensional representation of the scene photographed; this representation will be in color if a color plate is used. If a lenticular sheet using hemicylindrical elongate lenticles is used instead of a fly's eye sheet, a similar three-dimensional image is seen, but this image has parallax in only one direction, across the length of the lenticles.
Unfortunately, because in Lippman's method the composite image has to be viewed from the same side of the lenticular screen as that on which the scene photographed originally stood, and because the image formed by the lenticles during exposure of the plate has undergone only a single inversion of each miniature image, the three-dimensional representation produced is pseudoscopic, that is to say the depth perception in the image is inverted so that the object appears "inside out". To overcome this problem, a number of variations of Lippman's method have been devised to achieve two inversions of each miniature image in order to provide an orthoscopic ("right side out") three-dimensional image; see, for example, U.S. Pat. No. 3,895,867. However, most of these variations of Lippman's method are complex, involving multiple exposures with a single camera, or multiple cameras or multi-lens cameras to record a plurality of views of the same object, and require extremely accurate registration of multiple images to provide a single three-dimensional image. Moreover, any method for producing three-dimensional images which relies upon conventional cameras necessarily requires the presence of a real object before the camera, and such a method is ill-adapted for producing three-dimensional images of a virtual object, since it is highly undesirable to have to produce a real copy of the virtual object merely in order to effect the imaging process.
Thus, there is a need for a method of producing a three-dimensional image of an object which can readily be applied to imaging of virtual objects without a need to first produce a real copy of the object.